Header size with -XX:-UseCompressedOops

[Thomas Stüfe]

Hi Stefan,

See
https://bugs.openjdk.java.net/browse/JDK-8241825

Cheers, Thomas

On Mon 11. Apr 2022 at 19:58, Stefan Reich <
stefan.reich.maker.of.eye at googlemail.com> wrote:

> Hi Thomas,
>
> oh! Never heard about that change. Now I know. And yes this changes the
> picture as expected.
>
> Thanks
>
> On Mon, 11 Apr 2022 at 19:28, Thomas Stüfe <thomas.stuefe at gmail.com>
> wrote:
>
>> Hi Stefan,
>>
>> I think you want to set CompressedClassPointers.
>>
>> There used to be a dependency between CompressedOops and
>> CompressedClassPointers - switching the former off switched the latter off
>> too - but that dependency is gone and these settings are now independent of
>> each other.
>>
>> Cheers, Thomas
>>
>> On Mon, Apr 11, 2022 at 6:57 PM Stefan Reich <
>> stefan.reich.maker.of.eye at googlemail.com> wrote:
>>
>>> Hi, quick question to the experts.
>>>
>>> Java object header size is 12 bytes with CompressedOOPS (have verified
>>> this
>>> many times).
>>>
>>> Now I did a test with -XX:-UseCompressedOops just for fun and found that
>>> headers are still 12 bytes?
>>>
>>> I verified this in two ways:
>>>
>>> a. using Unsafe.objectFieldOffset
>>> b. making a whole lot of identical objects and measuring heap use before
>>> and after (with calls to System.gc)
>>>
>>> Both these methods give me a size of 16 bytes for an object with a single
>>> int field.
>>>
>>> How is this possible?
>>>
>>> Many greetings
>>> Stefan Reich
>>>
>>> --
>>> == Gaz.AI ==
>>>
>>
>
> --
> == Gaz.AI ==
>